There are a wide variety of metal covers that have been used in the construction industry to provide a building's outermost barrier to wind and water. They may be manufactured to resemble wood shake, slate, shingles, clay tiles or other non-metallic cover materials and may be installed on exterior walls or on roofs. More typically, however, metal covers for roofs are metal panel covers, that is, they utilize rather elongated metal panels installed along the slope of a roof.
Metal panel roofs utilize various flashings and other components where the fields of a roof terminate or intersect, such as the eaves, gables, valleys, ridges, and hips of a roof. Even in roofs having many different intersecting or overlapping fields, however, the basic construction of metal panel roofs across the major expanse of a roof is fairly standard. Most commonly, an array of spaced, elongated support members or “purlins” is mounted across the structural rafters of a roof substructure. The purlins run horizontally across the rafters, i.e., across the slope of the roof. Layers of insulation and various barriers may be, and for climate controlled buildings usually are installed. Decking also may be provided for additional support. A cover is provided by a series of rather elongated, mostly flat, interconnected metal panels.
Each cover panel is typically about a foot to three feet in width. Though they may be cut to any length, they commonly are 30 to 40 feet long and may run as long as 200 feet. The lateral edges of the panels are bent in various configurations to form upwardly extending sides and a trough in the middle. The trough is where most of the water will be shed from the roof. Adjacent panels are joined along their upwardly extending sides to create relatively narrow seams which are elevated above the trough. The panels are laid out such that the seams run vertically, i.e., with the slope of the roof. The panels also may have one or more ridges running vertically through the trough, and it is those vertically oriented seams and ridges that create the distinctive appearance that consumers associate with metal roofs. More importantly, however, since the seams between adjacent panels are formed a few inches above the troughs where most rain will be shed, metal panel roofs can be very resistant to leaking.
Raised-seam, metal panel roof covers may be classified according to the manner in which the panels are secured to the purlins. So called “through panel” or “exposed” fastener covers are characterized by the use of screws or other fasteners that penetrate through the cover panels. The panels typically are laid over a roof so that their sides overlap and form a raised, often trapezoidal shaped seam or “lap” rib. The panels then are joined together along the lap rib by, e.g., gasketed screws. Gasketed screws also are driven through the trough to fasten the panels to the purlins. Leakage around the fastener, at least initially, is not a significant problem. Over time, however, the elastomeric material from which the screw gaskets are fabricated can deteriorate, and leaks tend to develop around penetrating fasteners.
“Standing seam” covers can provide better resistance to leakage over longer periods of time, even for relatively flat roofs where ponding water is a concern and, in the eyes of many beholders, provide a more beautiful roof. Standing seam covers use concealed clips to secure the panels to the underlying purlins instead of unsightly and leak-prone penetrating fasteners. For example, individual panel clips may be installed in vertical lines from one purlin to the next along what will become a seam line between panels. Panels are then installed between the vertical lines of clips, with the upturned seam edges of the panels abutting and mating with the clips and each other. There are no penetrations through the panels when clips are used. Moreover, all gaps between the panels and the clips are elevated well above the trough through which most water runoff occurs. Thus, standing seam panel covers provide better, longer resistance to leakage as compared to covers using screws or other “through panel” fasteners that penetrate the panels.
Providing adequate uplift resistance, however, can be a greater challenge in standing seam panel covers. That is, most damage to roof covers is caused by wind blowing over the surface of the roof. That air flow forms low pressure areas over the roof and creates an uplift force in much the same way that the wing of an aircraft creates lift forces. While such forces are essential for flight, the uplift forces created by powerful winds over a roof can peel metal panels or other roof coverings away from the roof. It is relatively easy to provide a sufficient number of fasteners in exposed fastener covers. Since they are connected only along their seam lines, however, providing a sufficiently secure connection for panels in a standing seam cover is more problematic.
In addition, not all parts of a roof experience the same uplift forces in a given wind. The exposed edges of a roof experience greater uplift forces, and a given surface or field of a roof may be divided into three zones in recognition of such differences. The “edge” zones include those areas within a certain distance, usually around 8 feet, of an eave or gable. If the pitch of a roof is greater than 2 inches per foot of slope, the areas adjacent the ridge and hip of the roof also are considered “edge” zones. The edge zones experience greater wind uplift pressures than most of the roof and typically constitute approximately 15% of a roof's surface. The greatest uplift pressures, however, are in the “corner” zones. Those are the areas where edge zones overlap, and they typically constitute approximately 5% of the surface of a roof. The “field” zone is the rest of the roof field and it constitutes approximately 80% of the roof surface. The field zone experiences the lowest wind uplift pressures. In any event, providing sufficient resistance to wind uplift has been an increasingly important consideration in roof design as property owners and insurers seek to minimize their potential losses from wind damage, especially in hurricane prone areas like the Gulf and lower Atlantic coast.
Examples of standing seam roof covers using non-penetrating clips are disclosed in U.S. Pat. No. 4,575,983 to H. Lott, Jr. et al. The panels disclosed therein are asymmetrical standing seam panels. Asymmetrical panels have mating male-female connections, each panel having a male connection formed in one side and a female connection formed in its other side. Thus, installation must proceed in a certain direction across the roof, and removal for repair must proceed in the opposite direction.
Symmetrical standing seam panels, however, have sides which are identical and are joined with a separate seam cover. Symmetrical panels, therefore, may be installed in either direction. A damaged panel also may be removed for replacement without removing any adjacent panels. Examples of symmetrical standing seam roof covers using non-penetrating individual clips are disclosed in U.S. Pat. No. 4,649,684 to L. Petree et al. Other covers, such as those disclosed in U.S. Pat. No. 6,354,045 to M Boone et al. and U.S. Pat. No. 5,737,892 to P. Greenberg, utilize individual and elongated, “continuous” clips that are mounted to and span adjacent purlins. While they are more costly than covers using asymmetrical panels, such symmetrical panel covers can offer improved leak protection, better uplift resistance, and longer service life.
Despite the improvements in both the quality of panels and methods of installation, however, many of the metal roofs installed in the past twenty to thirty years have deteriorated to the point where they must be replaced. Removing an existing roof, however, is expensive and highly disruptive for occupants of a building. It also creates large quantities of waste that must be disposed of, and eliminates not only the existing roof, but whatever insulation value the existing roof may have provided. Thus, various covers have been developed to essentially recover an existing roof.
The most economical fix is to simply apply a plastic coating to the roof. Any exposed fasteners, along with seams, penetrations, flashing and the like, typically are caulked or covered with a fabric tape. All surfaces then are primed and the coating, usually a water based acrylic elastomer or a solvent-based butyl rubber or silicone rubber, is applied. Coatings have limited service lives, but have a great cost advantage.
So-called “single ply” covers offer a somewhat better solution at somewhat higher, but still relatively low cost. Rigid foam panels are laid between the seams of the existing metal panel roof. A recovery board, usually plywood, particle board, oriented strand (OSB) board, or fiber reinforced gypsum board, is installed over the foam panels. A rubber sheet, such as an ethylene propylene diene monomer (EPDM), thermoplastic polyolefin (TPO), polyvinyl chloride (PVC), ketone ethylene ester (KEE), such as Elvaloy™, is then adhered to the recovery board.
Another approach has been to install new metal panels over existing metal panel roofs. Installing a new metal cover, or “recover” over an existing cover offers significantly longer service life. Nevertheless, because that extended service life come with a much greater cost, metal panel recovers, especially standing seam metal panel recovers remain at a significant disadvantage relative to cheaper alternatives.
That increased cost is derived largely from the complexity of standing seam metal recovers and the cost of their various components. For example, standing seam metal recovers most commonly require the installation of new purlins over the existing roof panels. The new purlins then provide a base to which new panels may be attached, either with exposed fasteners or with clips.
In one common recover, for example, brackets are attached to the existing purlins, and a new purlin is mounted on the brackets above each existing purlin. A simpler recover, such as that disclosed in U.S. Pat. No. 5,367,848, uses notched purlins, the notches accommodating the seams and ridges in existing panels so that new purlins may be attached directly to existing purlins without brackets. Needlessly complicated recovers also have been devised, however, such as those disclosed in U.S. Pat. No. 8,061,087 and U.S. Pat. No. 8,327,590 to G. Ray. The recovers disclosed in Ray '087 and '590 require the installation of even more purlins above and between the purlins in the existing roof. In any event, new panels are attached to the new purlins, preferably with panel clips.
Recover systems have been developed, however, that do not rely on installation of new purlins over an existing cover. Clips are mounted to the existing purlins through the existing cover panels. Some systems have used “individual” clips, i.e., clips that mounted to a single purlin, and asymmetrical recover panels. Another recover system which does not rely on installing new purlins is disclosed in applicant's pending patent application, U.S. Ser. No. 13/573,282, filed Sep. 7, 2012. That application discloses a recover system which utilizes individual panel clips and “continuous” clips, i.e., relatively elongated clips that span at least two purlins. Both the individual and continuous clips are mounted to the existing purlins through the existing cover panels. Recover panels then are installed on the clips.
Such approaches can offer significant material savings, but they have drawbacks. Some of the material savings derived by eliminating new purlins is offset by the increased material cost of the clips. The clips typically are mounted in the trough of the existing cover panels, and other factors being equal, they necessarily will be taller than clips designed for mounting atop new purlins.
It also may not be easy to attach clips to existing purlins. The surface of existing panels, especially in the trough areas, may be uneven, making it more difficult to align an array of clips. Insulation also may be installed between the purlins and panels in an existing roof. The presence of such insulation not only makes it more likely that an aging roof will have surface irregularities, but it also may mean that the existing roof cannot provide adequate support for individual panel clips. That is especially true as the thickness of an insulation layer increases and its load capacity decreases. When a clip is a subjected to forces having even a relatively small horizontal component, relatively high torque forces may transmitted to the base of the clip, which can create harmful flexing and stress in a panel installed above thick, soft insulation.
Any system for installing a new metal panel roof cover, of course, also must provide sufficient wind uplift resistance. Moreover, all components should be designed with consideration of not only the cost of manufacturing the component, but also in view of how easily the component and the overall system may be installed and repaired. Material and labor costs are a major component of any roofing project. This is especially critical because there are so many cheaper, albeit less effective, recovering systems on the market.
The statements in this section are intended to provide background information related to the invention disclosed and claimed herein. Such information may or may not constitute prior art. It will be appreciated from the foregoing, however, that there remains a need for new and improved systems, apparatus and methods for installing metal panels over existing metal roofs. Such disadvantages and others inherent in the prior art are addressed by various aspects and embodiments of the subject invention.